光纤布拉格光栅波长解调系统的研制

光纤布拉格光栅波长解调系统利用光纤光栅的平均折射率和栅格周期对外界参量的敏感特性,将外界参量的变化转化为其布拉格波长的移动,通过解调布拉格波长的偏移来确定待测物理量的变化。采用波分复用技术构成光纤光栅传感网络,提出了由光源、布拉格光栅传感网络、光栅波长检测电路构成FBG波长解调系统的硬件设计方案。利用LabVIEW丰富的功能函数库,设计光纤布拉格光栅波长解调系统软件的各功能模块。最后在室内进行了FBG波长解调系统的调试实验。结果表明：在相同测试环境下,传感器的测试波长变化较稳定,数据的重复性较好,系统软硬件运行稳定可靠。     

矿物解理属性在宝石鉴定中的应用

解理面反光和光泽、解理的完全度、解理面组数及其夹角、解理的空间形态、解理面反光与矿物粒度的关系等构成了矿物解理的属性，这些属性在不同种的宝石矿物或同种宝石矿物各个体中性质不同，因此可应用于宝石的鉴定，尤其肉眼对翡翠鉴别时起到关键作用。     

Small angle neutron scattering by opals

Micro- and non-crystalline opals, chalcedony and flint show diffuse small angle neutron scattering (SANS). Precious opals give rise to two additional intensity maxima at very small scattering angles which are due to Bragg reflections from the closest packed non-crystalline silica spheres. A small angle texture diagram reveals that the closest packing is faulty. Synthetic non-crystalline opals yield much less intense small angle scattering due to lower contrast between silica spheres and interstitial cement or particles; in this case intensity maxima were not observed. The outer part of the scattering curves of opal-CT and microcrystalline quartz deviates from Porod's law. The specific surface of natural non-crystalline opals ranges from 0.006 to 0.018 nm^–1. In microcrystalline opals, the specific surface is about 10 times larger than in non-crystalline opals.     

双膜式光纤Bragg光栅土压力传感器的研究

采用双膜油腔结构研制了一种双膜式光纤Bragg光栅土压力传感器,偏压试验表明,此土压力传感器有效改善了与土压力传感器接触部分土压力分布不均的问题。在土压力的作用下,一次膜片变形产生的压力经传压油传递给二次膜片,传压杆与等强度悬臂梁刚性连接,二次膜片中心发生的挠度变化推动传压杆,使等强度悬臂梁的自由端发生同样大小的挠度变化。通过检测粘贴于等强度悬臂梁表面中心轴线上的光纤Bragg光栅的波长移位可获得土压力。载荷试验表明,传感器的灵敏度为 412.7 pm/MPa,非线性误差为1.97%FS,重复性误差为3.68%FS。     

光纤光栅应变传感器在地质灾害上的应用

根据光纤光栅传感的原理,提出了光纤光栅式封装应变传感器,对其传感特性进行了研究,并进行了室内实验。结合光栅传感监测滑坡的应用实例,探讨了光纤布拉格光栅传感元件在滑坡体上的布设工艺及监测过程。分析初期的监测结果,针对监测系统可能出现的问题提出了解决途径。     

Lattice dynamical calculations of anisotropic temperature factors of atoms in quartz,and the structure of β-quartz

Temperature factors for oxygen and silicon atoms in β-quartz were calculated on a Born-von Karman lattice dynamical model of an ordered structure. The calculated thermal ellipsoids were in excellent agreements with those of the previous structure refinements of the order model, for both magnitudes and orientations of the principal axes. The temperature factors are contributed mainly by the soft optic modes in Γ-M and the lowest-lying acoustic modes along Γ-A, which are also strongly temperature-dependent. The cusp-shaped temperature dependence of mean square displacements, 〈u²〉, of oxygen atom, observed previously around the α-β transition, are resulted from the softening of these modes. The temperature-dependent modes in Γ-A were also found to cause diffuse scattering extending along ±c^* of the fourth hexagon of the hk0 reciprocal lattice plane. The negative expansion known in β-quartz were interpreted in terms of asymmetrical forces exerting on oxygen atoms in Si-O-Si bending modes. In β-quartz, librational motions of oxygen atoms around Si-Si lines with large amplitudes, whose center is just on the β-position of high symmetry, must be possible under the condition that bending tetrahedral O-Si-O angles is energetically more favourable than compressing or stretching Si-O bonds.     

Electrons in feldspar II: a consideration of the influence of conduction band-tail states on luminescence processes

 Most natural feldspars contain many charged impurities, and display a range of bond angles, distributed about the ideal. These effects can lead to complications in the structure of the conduction band, giving rise to a tail of energy states (below the high-mobility conduction band) through which electrons can travel, but with reduced mobility: transport through these states is expected to be thermally activated. The purpose of this article is twofold. Firstly, we consider what kind of lattice perturbations could give rise to both localized and extended conduction band-tail states. Secondly, we consider what influence the band tails have on the luminescence properties of feldspar, where electrons travel through the sample prior to recombination. The work highlights the dominant role that 0.04–0.05-eV phonons play in both the luminescence excitation and emission processes of these materials. It also has relevance in the dating of feldspar sediments at elevated temperatures. Received: 11 May 2001 / Accepted: 6 September 2001     

Characterization of synthetic nanocrystalline mackinawite: crystal structure, particle size, and specific surface area

Iron sulfide was synthesized by reacting aqueous solutions of sodium sulfide and ferrous chloride for 3 days. By X-ray powder diffraction (XRPD), the resultant phase was determined to be primarily nanocrystalline mackinawite (space group: P4/ nmm) with unit cell parameters a = b = 3.67 Å and c = 5.20 Å. Iron K-edge XAS analysis also indicated the dominance of mackinawite. Lattice expansion of synthetic mackinawite was observed along the c-axis relative to well-crystalline mackinawite. Compared with relatively short-aged phase, the mackinawite prepared here was composed of larger crystallites with less elongated lattice spacings. The direct observation of lattice fringes by HR-TEM verified the applicability of Bragg diffraction in determining the lattice parameters of nanocrystalline mackinawite from XRPD patterns. Estimated particle size and external specific surface area (SSA_ext) of nanocrystalline mackinawite varied significantly with the methods used. The use of Scherrer equation for measuring crystallite size based on XRPD patterns is limited by uncertainty of the Scherrer constant (K) due to the presence of polydisperse particles. The presence of polycrystalline particles may also lead to inaccurate particle size estimation by Scherrer equation, given that crystallite and particle sizes are not equivalent. The TEM observation yielded the smallest SSA_ext of 103 m²/g. This measurement was not representative of dispersed particles due to particle aggregation from drying during sample preparation. In contrast, EGME method and PCS measurement yielded higher SSA_ext (276-345 m²/g by EGME and 424 ± 130 m²/g by PCS). These were in reasonable agreement with those previously measured by the methods insensitive to particle aggregation.     

Faults and Source Parameters of Earthquakes in the Baikal Rift Zone: Dip Angles of Fault Planes

Analysis of gentle, intermediate, and steep dip angles of fault planes in earthquake sources of the Baikal region is carried out with the slips in seismic sources being taken into account. The areas where normal faulting slips at steep, intermediate, and gentle angles took place are distinguished, and this can be interpreted as transformation of a steep dip to gentle one. It is found that the increase in energy class is accompanied by the number of earthquakes with steep dip angles, whereas the proportion of earthquakes with intermediate angles decreases, and the fraction of earthquakes with gentle angles remains quasi-stable and small.     

Measurement of Areas on a Sphere Using Fibonacci and Latitude–Longitude Lattices

The area of a spherical region can be easily measured by considering which sampling points of a lattice are located inside or outside the region. This point-counting technique is frequently used for measuring the Earth coverage of satellite constellations, employing a latitude–longitude lattice. This paper analyzes the numerical errors of such measurements, and shows that they could be greatly reduced if the Fibonacci lattice were used instead. The latter is a mathematical idealization of natural patterns with optimal packing, where the area represented by each point is almost identical. Using the Fibonacci lattice would reduce the root mean squared error by at least 40%. If, as is commonly the case, around a million lattice points are used, the maximum error would be an order of magnitude smaller.     

Radiation induced lattice defects in natural zircon (ZrSiO4) observed at atomic resolution

Fission tracks and point defects in natural zircon are directly observed by a 1 MV electron microscope at atomic resolution for three types of samples adjusted to the 100 orientation. Lattice planes intersecting the fission tracks at high angles are distorted in a rather irregular manner over a wide region up to more than 100 Å wide. Diameter of the tracks, ranging from 25 Å to 40Å, is much narrower than those so far reported for the U-doped synthetic zircon (100–200 Å), UO₂ thin film (100 Å), mica (66 Å, 240 Å) or fluorophlogopite (150 Å). The fact that fairly long tracks thousands of angstroms in length are observed in thin 100-oriented sample hundreds of angstroms in thickness and that some of them are nearly parallel to a low index lattice plane suggest a possible occurrence of channelling in the process of track formation. Parallel tracks often observed in chemically etched specimens support the idea of channelling. Slightly bent tracks are sometimes observed. It is concluded from computer simulation that many contrast anomalies of bright and dark spots in the lattice image are due to point defects of vacancies and interstitial atoms, mainly produced by the direct atomic collision with α-particles or by passage of ionizing nuclear particles. Optimum conditions of the observation of point defects with highest contrast are studied. One interstitial Zr atom or one Zr ion vacancy will give very low contrast and will be not detectable unless the crystal is less than two unit cells thick. A pair of Zr ion vacancies, however, yields extended detectable limit of thickness. Some of the observed defects are in good accordance with those simulated.     

光纤光栅传感技术在PHC管桩中不同埋设工艺试验研究

通过在同一现场针对光纤光栅传感技术在预应力高强混凝土管桩（PHC桩）测试中的应用,采用桩身表面开槽和桩身内植入的两种不同埋设工艺,进行了PHC管桩的贯入对比试验,比较了两种埋设工艺的桩身应力分布情况、桩端阻力的异同,试验研究发现:两种埋设工艺桩身轴力都随贯入深度增加而减小,桩身轴力传递速度相近,都具有相近的斜率,采用桩身内植入埋设工艺小于采用桩身表面开槽埋设工艺桩端阻力测试数据,但两者的相差幅度较小。PHC管桩桩身植入的埋设工艺光纤光栅传感器存活率较高,数据可靠,可以应用在PHC管桩的应力测试中。     

岩石单轴压缩光纤光栅传感检测方法研究

通过在岩石试件表面粘贴光栅与应变片的方法,测试了岩石单轴加载过程中轴向、环向的应变变化。将测试结果相对照,研究了光纤传感技术在岩石变形检测中的应用。加载方式为循环加载,最后一次至试件破裂,仅测试试件破裂前小变形阶段的变形。3次加载后结果显示光栅与应变片的测试结果一致,二者数据相吻合,证明光纤光栅传感技术可以应用于岩石试件变形检测中,对于提高岩石变形的测试手段具有一定的意义。     

Sigmoidal exsolution by internal shear stress in pyroxenes from chondritic meteorites

Pyroxenes of pigeonitic and augitic bulk compositions in H3–4 chondritic meteorites commonly exhibit sigmoidal precipitates, rather than the elsewhere common lamellar associations. Most often, submicrometric sigmoids with calcic clinopyroxene composition occur within clinoenstatite; more rarely, clinoenstatite sigmoids occur within calcic clinopyroxene. The sigmoids appear as 001 terminated lamellae, with terminations rotated in opposite directions towards the 100 orientation. Pre-exsolution pigeonite and augite formed at temperatures higher than 980 °C, whereas sigmoidal exsolution occurred between 990 and 830 °C. Local anomalous lattice parameters determined by electron diffraction suggest that lattice parameters are most strained where the exsolution texture is most poorly defined. Shear strain occurs during exsolution due to mismatching lattice parameters and variable angles. In response to shear stress, the lamellae relax and assume sigmoidal strained morphologies. Sigmoidal exsolution is strongly controlled by (100) orthoenstatite stacking faults that possibly trigger exsolution.     

The crystal and magnetic structure of Li-aegirine LiFe3+Si2O6: a temperature-dependent study

Single crystals of Li-aegirine LiFe³⁺Si₂O₆ were synthesized at 1573?K and 3?GPa, and a polycrystalline sample suitable for neutron diffraction was produced by ceramic sintering at 1223?K. LiFe³⁺Si₂O₆ is monoclinic, space group C2/c, a=9.6641(2)?Å, b= 8.6612(3)?Å, c=5.2924(2)?Å, β=110.12(1)^° at 300?K as refined from powder neutron data. At 229?K Li-aegirine undergoes a phase transition from C2/c to P2₁ /c. This is indicated by strong discontinuities in the temperature variation of the lattice parameters, especially for the monoclinic angle β and by the appearance of Bragg reflections (hkl) with h+k≠2n. In the low-temperature form two non-equivalent Si-sites with 〈SiA–O〉=1.622?Å and 〈SiB–O〉=1.624?Å at 100?K are present. The bridging angles of the SiO₄ tetrahedra O3–O3–O3 are 192.55(8)° and 160.02(9)° at 100?K in the two independent tetrahedral chains in space group P2₁ /c, whereas it is 180.83(9)° at 300?K in the high-temperature C2/c phase, i.e. the chains are nearly fully expanded. Upon the phase transition the Li-coordination changes from six to five. At 100?K four Li–O bond lengths lie within 2.072(4)–2.172(3)?Å, the fifth Li–O bond length is 2.356(4)?Å, whereas the Li–O3?A bond lengths amount to 2.796(4)?Å. From ⁵⁷Fe Mössbauer spectroscopic measurements between 80 and 500?K the structural phase transition is characterized by a small discontinuity of the quadrupole splitting. Temperature-dependent neutron powder diffraction experiments show first occurrence of magnetic reflections at 16.5?K in good agreement with the point of inflection in the temperature-dependent magnetization of LiFe³⁺Si₂O₆. Distinct preordering phenomena can be observed up to 35?K. At the magnetic phase transition the unit cell parameters exhibit a pronounced magneto-striction of the lattice. Below T _N Li-aegirine shows a collinear antiferromagnetic structure. From our neutron powder diffraction experiments we extract a collinear antiferromagnetic spin arrangement within the a–c plane.     

Thermal expansion of kyanite at ambient pressure: An X-ray powder diffraction study up to 1000 ℃

The thermal expansion coefficients of kyanite at ambient pressure have been investigated by an X-ray powder diffraction technique with temperatures up to 1000 ℃. No phase transition was observed in the experimental temperature range. Data for the unit-cell parameters and temperatures were fitted empirically resulting in the following thermal expansion coefficients: aa = 5.8(3) × 10-5, ab = 5.8 (1) × 10-5, ac% = 5.2(1) × 10-5, and av = 7.4(1) × 10-3 ℃-1, in good agreement with a recent neutron powder diffraction study. On the other hand, the variation of the unit-cell angles a, β and γ of kyanite with increase in temperature is very complicated, and the agreement among all studies is poor. The thermal expansion data at ambient pressure reported here and the compression data at ambient temperature from the literature suggest that, for the kyanite lattice, the most and least thermally expandable directions correspond to the most and least compressible directions, respectively.     

预应力锚索格构梁作用下边坡土中应力分布的室内模型试验研究

预应力锚索格构梁由于其多方面的优点而在工程中得到了广泛的应用。但到目前为止，对预应力锚索格构梁的设计计算还没有提出一个合理的计算模型。本文针对现有计算模型对格梁底部地基反力的分布假设的不足，进行了预应力锚索格构梁的室内模型试验，并对格梁底部土体应力的实际分布情况进行了分析。分析结果显示，土中应力随锚索预应力的增大而增大，且格梁底部的基底反力并非成直线或线性变化，而是与所加锚索的位置有关，因此不能简单地将格构梁看成刚性梁。最后，就本模型试验所存在的不足对今后的研究方向提出了几点建议。     

碳纤维布用于格构缺陷修复技术的模型试验研究

格构锚固是边（滑）坡工程常用的防治技术之一,长期服役的格构梁通常会产生局部破损的现象,影响边（滑）坡长期稳定性,而贴附碳纤维布是修复格构梁缺陷最行之有效的手段。采用室内模型试验槽填筑黏土方式模拟滑坡体,设计相似比为1:10的格构梁,通过千斤顶施加滑坡推力,开展碳纤维布用于格构缺陷修复技术的模型试验,监控格构梁后部土压力、格梁应力、格梁位移等参数,分析碳纤维布修复前后格构梁和碳纤维布两者的荷载分担比、钢筋应力改善情况和格梁弯矩的前后变化规律。试验数据分析表明,碳纤维布和格构梁荷载分担比得到了改善,滑坡推力作用在碳纤维布和格构梁复合体时,碳纤维布先于格构梁受力,并且受力远远大于格构梁,碳纤维布所承受的荷载分担比约为83%;格梁破坏首先为受拉破坏,然后为受压破坏;模型试验中,在钢筋表面粘贴了应变片,监测到钢筋的应变情况,碳纤维布修复后钢筋受力得到改善,修复后的最大钢筋应力比修复前降低了8倍多;对修复前后,格构梁弯矩变化进行了研究,碳纤维布修复后格梁弯矩显著降低,约为修复前的1/10-1/3。鉴于以上研究结果,说明碳纤维布用于修复、加固缺陷格构梁工程效果显著。     

光纤传感技术在锚杆轴力监测中的应用

在简述了光纤Bragg光栅传感器基本工作原理的基础上,通过沪―蓉―西高速公路龙潭隧道支护锚杆轴力监测的工程应用,探讨研究了光纤传感技术用于岩土工程监测的几个重要环节--传感器选择、传感器安装、传感器标定及传感器埋设。通过现场监测获得了复杂地质条件下特长隧道支护锚杆轴力的变化特性,为光纤传感技术在岩土工程监测领域的应用积累了一定的经验。